Electric power steering apparatus

Abstract

An electric power steering apparatus is provided in which stably performing drive of FETs of an inverter can be achieved by means of a simplified constitution. The electric power steering apparatus drive-controls a motor through an inverter comprised of an FET bridge based on each-phase duty command values of pulse-width modulation (PWM) and perform assist control of a steering system. The electric power steering apparatus comprises a charge pump circuit and a bootstrap circuit that generate a booster power voltage for driving upper-FETs of the FET bridge, wherein the circuit having a higher voltage is used as the booster power voltage.

The invention claimed is: 
     
       1. An electric power steering apparatus that calculates each-phase duty command values of PWM, based on said each-phase duty command values, drives upper-FETs of an FET bridge through an upper-FET gate driving section and drives lower-FETs of said FET bridge through a lower-FET gate driving section, and performs an assist control of a steering system by drive-controlling a motor with an inverter comprised of said FET bridge, comprising:
 a charge pump circuit and a bootstrap circuit that are connected to said upper-FET gate driving section and are connected with each other through diodes, 
 a voltage from one having a high voltage of said charge pump circuit and said bootstrap circuit is used as a booster power voltage to drive said upper-FETs, 
 in response to a failure of said charge pump circuit is determined, said upper-FETs of said FET bridge is driven by using a voltage generated at said bootstrap circuit and said assist control is continued, and 
 wherein said upper-FET gate driving section is configured to control said upper-FETs and said lower-FET gate driving section is configured to control said lower-FETs. 
 
     
     
       2. An electric power steering apparatus according to  claim 1 , wherein determination of said failure of said charge pump circuit is performed based on a system voltage and an output voltage of said charge pump circuit. 
     
     
       3. An electric power steering apparatus according to  claim 2 , wherein when said failure of said charge pump circuit is determined, each-phase duty command values of said upper-FETs are limited. 
     
     
       4. An electric power steering apparatus according to  claim 1 , wherein
 said charge pump circuit is connected to a first diode and said bootstrap circuit is connected to a second diode, and 
 said first diode and said second diode are connected with each other and are further connected to said upper-FET gate driving section. 
 
     
     
       5. An electric power steering apparatus according to  claim 4 , wherein
 said first diode and said second diode are connected with each other in a reverse direction.